Immunological approaches to measure DNA damage caused by carcinogens may be useful in biochemical epidemiology studies to identify individuals at high cancer risk. Mouse myeloma cells (P3x63) were fused with spleen cells from Balb/c mice immunized with aflatoxin B1-DNA adducts. Hybrid cells were grown in selective medium and tested for production of antibody-secreting hybridomas. Clones secreting monoclonal antibodies binding specifically to aflatoxin B1-DNA adducts have been obtained. These antibodies have been characterized and, in conjunction with competitive ultrasensitive enzyme immunoassay, used to quantitate aflatoxin B1 modified DNA in liver obtained from rats administered dosages ranging from 0.01-1.0 mg AFB1/Kg. At this time, the limit of sensitivity is one aflatoxin B1 residue per 1,355,000 nucleotides. Monoclonal antibodies to other carcinogen-DNA adducts are also being prepared.